A Chiral Adamantanophane: Preparation, Enantiomer Separation, Theoretical and Experimental Circular Dichroism and Absolute Configuration

Exchange of aromatic units (e.g. benzene) for aliphatic/ali‐cyclic building blocks (e.g. adamantane) in cyclophanes leads to molecules of the “araliphane” type. The synthesis of the highly strained [2.2](1,3)adamantanometacyclophanes 5a–c is described. The cyclophane skeletons of these molecules are conformationally rigid and therefore 5a–c are planar‐chiral. The circular dichroism of 5c has been calculated theoretically with NDDO/MRD‐CI methods and was measured. Agreement of theory and experiment is good, a comparison of both allows the assignment of the absolute configuration of the two enantiomers of 5c with high probability. Furthermore, analysis of the nπ* band in the CD spectrum yields a, simple general rule to determine the conformation of the carboxyl group in phenyl ester substructures. Theoretical calculations of the strain energy (Es) of 5c reveal the distribution of strain within the molecule.